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+      #
+      #
       # Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Google Inc.
+      #
       # This program is free software; you can redistribute it and/or modify
       # it under the terms of the GNU General Public License as published by
       # the Free Software Foundation; either version 2 of the License, or
       # (at your option) any later version.
+      #
       # This program is distributed in the hope that it will be useful, but
       # WITHOUT ANY WARRANTY; without even the implied warranty of
       # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
       # General Public License for more details.
+      #
       # You should have received a copy of the GNU General Public License
       # along with this program; if not, write to the Free Software
       # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
       # 02110-1301, USA.
       """Module implementing the Ganeti locking code."""
       # pylint: disable=W0212
       # W0212 since e.g. LockSet methods use (a lot) the internals of
       # SharedLock
       import os
       import select
       import threading
       import errno
       import weakref
       import logging
       import heapq
       import itertools
       import time
       from ganeti import errors
       from ganeti import utils
       from ganeti import compat
       from ganeti import query
       _EXCLUSIVE_TEXT = "exclusive"
       _SHARED_TEXT = "shared"
       _DELETED_TEXT = "deleted"
       _DEFAULT_PRIORITY = 0
       #: Minimum timeout required to consider scheduling a pending acquisition
       #: (seconds)
       _LOCK_ACQUIRE_MIN_TIMEOUT = (1.0 / 1000)
       # Internal lock acquisition modes for L{LockSet}
       (_LS_ACQUIRE_EXACT,
        _LS_ACQUIRE_ALL,
        _LS_ACQUIRE_OPPORTUNISTIC) = range(1, 4)
       _LS_ACQUIRE_MODES = compat.UniqueFrozenset([
         _LS_ACQUIRE_EXACT,
         _LS_ACQUIRE_ALL,
         _LS_ACQUIRE_OPPORTUNISTIC,
         ])
       def ssynchronized(mylock, shared=0):
         """Shared Synchronization decorator.
         Calls the function holding the given lock, either in exclusive or shared
         mode. It requires the passed lock to be a SharedLock (or support its
         semantics).
         @type mylock: lockable object or string
         @param mylock: lock to acquire or class member name of the lock to acquire
         """
         def wrap(fn):
           def sync_function(*args, **kwargs):
             if isinstance(mylock, basestring):
               assert args, "cannot ssynchronize on non-class method: self not found"
               # args[0] is "self"
               lock = getattr(args[0], mylock)
             else:
               lock = mylock
             lock.acquire(shared=shared)
             try:
               return fn(*args, **kwargs)
             finally:
               lock.release()
           return sync_function
         return wrap
       class _SingleNotifyPipeConditionWaiter(object):
         """Helper class for SingleNotifyPipeCondition
         """
         __slots__ = [
           "_fd",
           "_poller",
+          ]
         def __init__(self, poller, fd):
           """Constructor for _SingleNotifyPipeConditionWaiter
           @type poller: select.poll
           @param poller: Poller object
           @type fd: int
           @param fd: File descriptor to wait for
           """
           object.__init__(self)
           self._poller = poller
           self._fd = fd
         def __call__(self, timeout):
           """Wait for something to happen on the pipe.
           @type timeout: float or None
           @param timeout: Timeout for waiting (can be None)
           """
           running_timeout = utils.RunningTimeout(timeout, True)
           while True:
             remaining_time = running_timeout.Remaining()
             if remaining_time is not None:
               if remaining_time < 0.0:
                 break
               # Our calculation uses seconds, poll() wants milliseconds
               remaining_time *= 1000
             try:
               result = self._poller.poll(remaining_time)
             except EnvironmentError, err:
               if err.errno != errno.EINTR:
                 raise
               result = None
             # Check whether we were notified
             if result and result[0][0] == self._fd:
               break
       class _BaseCondition(object):
         """Base class containing common code for conditions.
         Some of this code is taken from python's threading module.
         """
         __slots__ = [
           "_lock",
           "acquire",
           "release",
           "_is_owned",
           "_acquire_restore",
           "_release_save",
+          ]
         def __init__(self, lock):
           """Constructor for _BaseCondition.
           @type lock: threading.Lock
           @param lock: condition base lock
           """
           object.__init__(self)
           try:
             self._release_save = lock._release_save
           except AttributeError:
             self._release_save = self._base_release_save
           try:
             self._acquire_restore = lock._acquire_restore
           except AttributeError:
             self._acquire_restore = self._base_acquire_restore
           try:
             self._is_owned = lock.is_owned
           except AttributeError:
             self._is_owned = self._base_is_owned
           self._lock = lock
           # Export the lock's acquire() and release() methods
           self.acquire = lock.acquire
           self.release = lock.release
         def _base_is_owned(self):
           """Check whether lock is owned by current thread.
           """
           if self._lock.acquire(0):
             self._lock.release()
             return False
           return True
         def _base_release_save(self):
           self._lock.release()
         def _base_acquire_restore(self, _):
           self._lock.acquire()
         def _check_owned(self):
           """Raise an exception if the current thread doesn't own the lock.
           """
           if not self._is_owned():
             raise RuntimeError("cannot work with un-aquired lock")
       class SingleNotifyPipeCondition(_BaseCondition):
         """Condition which can only be notified once.
         This condition class uses pipes and poll, internally, to be able to wait for
         notification with a timeout, without resorting to polling. It is almost
         compatible with Python's threading.Condition, with the following differences:
           - notifyAll can only be called once, and no wait can happen after that
           - notify is not supported, only notifyAll
         """
         __slots__ = [
           "_poller",
           "_read_fd",
           "_write_fd",
           "_nwaiters",
           "_notified",
+          ]
         _waiter_class = _SingleNotifyPipeConditionWaiter
         def __init__(self, lock):
           """Constructor for SingleNotifyPipeCondition
           """
           _BaseCondition.__init__(self, lock)
           self._nwaiters = 0
           self._notified = False
           self._read_fd = None
           self._write_fd = None
           self._poller = None
         def _check_unnotified(self):
           """Throws an exception if already notified.
           """
           if self._notified:
             raise RuntimeError("cannot use already notified condition")
         def _Cleanup(self):
           """Cleanup open file descriptors, if any.
           """
           if self._read_fd is not None:
             os.close(self._read_fd)
             self._read_fd = None
           if self._write_fd is not None:
             os.close(self._write_fd)
             self._write_fd = None
           self._poller = None
         def wait(self, timeout):
           """Wait for a notification.
           @type timeout: float or None
           @param timeout: Waiting timeout (can be None)
           """
           self._check_owned()
           self._check_unnotified()
           self._nwaiters += 1
           try:
             if self._poller is None:
               (self._read_fd, self._write_fd) = os.pipe()
               self._poller = select.poll()
               self._poller.register(self._read_fd, select.POLLHUP)
             wait_fn = self._waiter_class(self._poller, self._read_fd)
             state = self._release_save()
             try:
               # Wait for notification
               wait_fn(timeout)
             finally:
               # Re-acquire lock
               self._acquire_restore(state)
           finally:
             self._nwaiters -= 1
             if self._nwaiters == 0:
               self._Cleanup()
         def notifyAll(self): # pylint: disable=C0103
           """Close the writing side of the pipe to notify all waiters.
           """
           self._check_owned()
           self._check_unnotified()
           self._notified = True
           if self._write_fd is not None:
             os.close(self._write_fd)
             self._write_fd = None
       class PipeCondition(_BaseCondition):
         """Group-only non-polling condition with counters.
         This condition class uses pipes and poll, internally, to be able to wait for
         notification with a timeout, without resorting to polling. It is almost
         compatible with Python's threading.Condition, but only supports notifyAll and
         non-recursive locks. As an additional features it's able to report whether
         there are any waiting threads.
         """
         __slots__ = [
           "_waiters",
           "_single_condition",
+          ]
         _single_condition_class = SingleNotifyPipeCondition
         def __init__(self, lock):
           """Initializes this class.
           """
           _BaseCondition.__init__(self, lock)
           self._waiters = set()
           self._single_condition = self._single_condition_class(self._lock)
         def wait(self, timeout):
           """Wait for a notification.
           @type timeout: float or None
           @param timeout: Waiting timeout (can be None)
           """
           self._check_owned()
           # Keep local reference to the pipe. It could be replaced by another thread
           # notifying while we're waiting.
           cond = self._single_condition
           self._waiters.add(threading.currentThread())
           try:
             cond.wait(timeout)
           finally:
             self._check_owned()
             self._waiters.remove(threading.currentThread())
         def notifyAll(self): # pylint: disable=C0103
           """Notify all currently waiting threads.
           """
           self._check_owned()
           self._single_condition.notifyAll()
           self._single_condition = self._single_condition_class(self._lock)
         def get_waiting(self):
           """Returns a list of all waiting threads.
           """
           self._check_owned()
           return self._waiters
         def has_waiting(self):
           """Returns whether there are active waiters.
           """
           self._check_owned()
           return bool(self._waiters)
         def __repr__(self):
           return ("<%s.%s waiters=%s at %#x>" %
                   (self.__class__.__module__, self.__class__.__name__,
                    self._waiters, id(self)))
       class _PipeConditionWithMode(PipeCondition):
         __slots__ = [
           "shared",
+          ]
         def __init__(self, lock, shared):
           """Initializes this class.
           """
           self.shared = shared
           PipeCondition.__init__(self, lock)
       class SharedLock(object):
         """Implements a shared lock.
         Multiple threads can acquire the lock in a shared way by calling
         C{acquire(shared=1)}. In order to acquire the lock in an exclusive way
         threads can call C{acquire(shared=0)}.
         Notes on data structures: C{__pending} contains a priority queue (heapq) of
         all pending acquires: C{[(priority1: prioqueue1), (priority2: prioqueue2),
         ...]}. Each per-priority queue contains a normal in-order list of conditions
         to be notified when the lock can be acquired. Shared locks are grouped
         together by priority and the condition for them is stored in
         C{__pending_shared} if it already exists. C{__pending_by_prio} keeps
         references for the per-priority queues indexed by priority for faster access.
         @type name: string
         @ivar name: the name of the lock
         """
         __slots__ = [
           "__weakref__",
           "__deleted",
           "__exc",
           "__lock",
           "__pending",
           "__pending_by_prio",
           "__pending_shared",
           "__shr",
           "__time_fn",
           "name",
+          ]
         __condition_class = _PipeConditionWithMode
         def __init__(self, name, monitor=None, _time_fn=time.time):
           """Construct a new SharedLock.
           @param name: the name of the lock
           @type monitor: L{LockMonitor}
           @param monitor: Lock monitor with which to register
           """
           object.__init__(self)
           self.name = name
           # Used for unittesting
           self.__time_fn = _time_fn
           # Internal lock
           self.__lock = threading.Lock()
           # Queue containing waiting acquires
           self.__pending = []
           self.__pending_by_prio = {}
           self.__pending_shared = {}
           # Current lock holders
           self.__shr = set()
           self.__exc = None
           # is this lock in the deleted state?
           self.__deleted = False
           # Register with lock monitor
           if monitor:
             logging.debug("Adding lock %s to monitor", name)
             monitor.RegisterLock(self)
         def __repr__(self):
           return ("<%s.%s name=%s at %#x>" %
                   (self.__class__.__module__, self.__class__.__name__,
                    self.name, id(self)))
         def GetLockInfo(self, requested):
           """Retrieves information for querying locks.
           @type requested: set
           @param requested: Requested information, see C{query.LQ_*}
           """
           self.__lock.acquire()
           try:
             # Note: to avoid unintentional race conditions, no references to
             # modifiable objects should be returned unless they were created in this
             # function.
             mode = None
             owner_names = None
             if query.LQ_MODE in requested:
               if self.__deleted:
                 mode = _DELETED_TEXT
                 assert not (self.__exc or self.__shr)
               elif self.__exc:
                 mode = _EXCLUSIVE_TEXT
               elif self.__shr:
                 mode = _SHARED_TEXT
             # Current owner(s) are wanted
             if query.LQ_OWNER in requested:
               if self.__exc:
                 owner = [self.__exc]
               else:
                 owner = self.__shr
               if owner:
                 assert not self.__deleted
                 owner_names = [i.getName() for i in owner]
             # Pending acquires are wanted
             if query.LQ_PENDING in requested:
               pending = []
               # Sorting instead of copying and using heaq functions for simplicity
               for (_, prioqueue) in sorted(self.__pending):
                 for cond in prioqueue:
                   if cond.shared:
                     pendmode = _SHARED_TEXT
                   else:
                     pendmode = _EXCLUSIVE_TEXT
                   # List of names will be sorted in L{query._GetLockPending}
                   pending.append((pendmode, [i.getName()
                                              for i in cond.get_waiting()]))
             else:
               pending = None
             return [(self.name, mode, owner_names, pending)]
           finally:
             self.__lock.release()
         def __check_deleted(self):
           """Raises an exception if the lock has been deleted.
           """
           if self.__deleted:
             raise errors.LockError("Deleted lock %s" % self.name)
         def __is_sharer(self):
           """Is the current thread sharing the lock at this time?
           """
           return threading.currentThread() in self.__shr
         def __is_exclusive(self):
           """Is the current thread holding the lock exclusively at this time?
           """
           return threading.currentThread() == self.__exc
         def __is_owned(self, shared=-1):
           """Is the current thread somehow owning the lock at this time?
           This is a private version of the function, which presumes you're holding
           the internal lock.
           """
           if shared < 0:
             return self.__is_sharer() or self.__is_exclusive()
           elif shared:
             return self.__is_sharer()
           else:
             return self.__is_exclusive()
         def is_owned(self, shared=-1):
           """Is the current thread somehow owning the lock at this time?
           @param shared:
               - < 0: check for any type of ownership (default)
               - 0: check for exclusive ownership
               - > 0: check for shared ownership
           """
           self.__lock.acquire()
           try:
             return self.__is_owned(shared=shared)
           finally:
             self.__lock.release()
         #: Necessary to remain compatible with threading.Condition, which tries to
         #: retrieve a locks' "_is_owned" attribute
         _is_owned = is_owned
         def _count_pending(self):
           """Returns the number of pending acquires.
           @rtype: int
           """
           self.__lock.acquire()
           try:
             return sum(len(prioqueue) for (_, prioqueue) in self.__pending)
           finally:
             self.__lock.release()
         def _check_empty(self):
           """Checks whether there are any pending acquires.
           @rtype: bool
           """
           self.__lock.acquire()
           try:
             # Order is important: __find_first_pending_queue modifies __pending
             (_, prioqueue) = self.__find_first_pending_queue()
             return not (prioqueue or
                         self.__pending or
                         self.__pending_by_prio or
                         self.__pending_shared)
           finally:
             self.__lock.release()
         def __do_acquire(self, shared):
           """Actually acquire the lock.
           """
           if shared:
             self.__shr.add(threading.currentThread())
           else:
             self.__exc = threading.currentThread()
         def __can_acquire(self, shared):
           """Determine whether lock can be acquired.
           """
           if shared:
             return self.__exc is None
           else:
             return len(self.__shr) == 0 and self.__exc is None
         def __find_first_pending_queue(self):
           """Tries to find the topmost queued entry with pending acquires.
           Removes empty entries while going through the list.
           """
           while self.__pending:
             (priority, prioqueue) = self.__pending[0]
             if prioqueue:
               return (priority, prioqueue)
             # Remove empty queue
             heapq.heappop(self.__pending)
             del self.__pending_by_prio[priority]
             assert priority not in self.__pending_shared
           return (None, None)
         def __is_on_top(self, cond):
           """Checks whether the passed condition is on top of the queue.
           The caller must make sure the queue isn't empty.
           """
           (_, prioqueue) = self.__find_first_pending_queue()
           return cond == prioqueue[0]
         def __acquire_unlocked(self, shared, timeout, priority):
           """Acquire a shared lock.
           @param shared: whether to acquire in shared mode; by default an
               exclusive lock will be acquired
           @param timeout: maximum waiting time before giving up
           @type priority: integer
           @param priority: Priority for acquiring lock
           """
           self.__check_deleted()
           # We cannot acquire the lock if we already have it
           assert not self.__is_owned(), ("double acquire() on a non-recursive lock"
                                          " %s" % self.name)
           # Remove empty entries from queue
           self.__find_first_pending_queue()
           # Check whether someone else holds the lock or there are pending acquires.
           if not self.__pending and self.__can_acquire(shared):
             # Apparently not, can acquire lock directly.
             self.__do_acquire(shared)
             return True
           # The lock couldn't be acquired right away, so if a timeout is given and is
           # considered too short, return right away as scheduling a pending
           # acquisition is quite expensive
           if timeout is not None and timeout < _LOCK_ACQUIRE_MIN_TIMEOUT:
             return False
           prioqueue = self.__pending_by_prio.get(priority, None)
           if shared:
             # Try to re-use condition for shared acquire
             wait_condition = self.__pending_shared.get(priority, None)
             assert (wait_condition is None or
                     (wait_condition.shared and wait_condition in prioqueue))
           else:
             wait_condition = None
           if wait_condition is None:
             if prioqueue is None:
               assert priority not in self.__pending_by_prio
               prioqueue = []
               heapq.heappush(self.__pending, (priority, prioqueue))
               self.__pending_by_prio[priority] = prioqueue
             wait_condition = self.__condition_class(self.__lock, shared)
             prioqueue.append(wait_condition)
             if shared:
               # Keep reference for further shared acquires on same priority. This is
               # better than trying to find it in the list of pending acquires.
               assert priority not in self.__pending_shared
               self.__pending_shared[priority] = wait_condition
           wait_start = self.__time_fn()
           acquired = False
           try:
             # Wait until we become the topmost acquire in the queue or the timeout
             # expires.
             while True:
               if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
                 self.__do_acquire(shared)
                 acquired = True
                 break
               # A lot of code assumes blocking acquires always succeed, therefore we
               # can never return False for a blocking acquire
               if (timeout is not None and
                   utils.TimeoutExpired(wait_start, timeout, _time_fn=self.__time_fn)):
                 break
               # Wait for notification
               wait_condition.wait(timeout)
               self.__check_deleted()
           finally:
             # Remove condition from queue if there are no more waiters
             if not wait_condition.has_waiting():
               prioqueue.remove(wait_condition)
               if wait_condition.shared:
                 # Remove from list of shared acquires if it wasn't while releasing
                 # (e.g. on lock deletion)
                 self.__pending_shared.pop(priority, None)
           return acquired
         def acquire(self, shared=0, timeout=None, priority=None,
                     test_notify=None):
           """Acquire a shared lock.
           @type shared: integer (0/1) used as a boolean
           @param shared: whether to acquire in shared mode; by default an
               exclusive lock will be acquired
           @type timeout: float
           @param timeout: maximum waiting time before giving up
           @type priority: integer
           @param priority: Priority for acquiring lock
           @type test_notify: callable or None
           @param test_notify: Special callback function for unittesting
           """
           if priority is None:
             priority = _DEFAULT_PRIORITY
           self.__lock.acquire()
           try:
             # We already got the lock, notify now
             if __debug__ and callable(test_notify):
               test_notify()
             return self.__acquire_unlocked(shared, timeout, priority)
           finally:
             self.__lock.release()
         def downgrade(self):
           """Changes the lock mode from exclusive to shared.
           Pending acquires in shared mode on the same priority will go ahead.
           """
           self.__lock.acquire()
           try:
             assert self.__is_owned(), "Lock must be owned"
             if self.__is_exclusive():
               # Do nothing if the lock is already acquired in shared mode
               self.__exc = None
               self.__do_acquire(1)
               # Important: pending shared acquires should only jump ahead if there
               # was a transition from exclusive to shared, otherwise an owner of a
               # shared lock can keep calling this function to push incoming shared
               # acquires
               (priority, prioqueue) = self.__find_first_pending_queue()
               if prioqueue:
                 # Is there a pending shared acquire on this priority?
                 cond = self.__pending_shared.pop(priority, None)
                 if cond:
                   assert cond.shared
                   assert cond in prioqueue
                   # Ensure shared acquire is on top of queue
                   if len(prioqueue) > 1:
                     prioqueue.remove(cond)
                     prioqueue.insert(0, cond)
                   # Notify
                   cond.notifyAll()
             assert not self.__is_exclusive()
             assert self.__is_sharer()
             return True
           finally:
             self.__lock.release()
         def release(self):
           """Release a Shared Lock.
           You must have acquired the lock, either in shared or in exclusive mode,
           before calling this function.
           """
           self.__lock.acquire()
           try:
             assert self.__is_exclusive() or self.__is_sharer(), \
               "Cannot release non-owned lock"
             # Autodetect release type
             if self.__is_exclusive():
               self.__exc = None
               notify = True
             else:
               self.__shr.remove(threading.currentThread())
               notify = not self.__shr
             # Notify topmost condition in queue if there are no owners left (for
             # shared locks)
             if notify:
               self.__notify_topmost()
           finally:
             self.__lock.release()
         def __notify_topmost(self):
           """Notifies topmost condition in queue of pending acquires.
           """
           (priority, prioqueue) = self.__find_first_pending_queue()
           if prioqueue:
             cond = prioqueue[0]
             cond.notifyAll()
             if cond.shared:
               # Prevent further shared acquires from sneaking in while waiters are
               # notified
               self.__pending_shared.pop(priority, None)
         def _notify_topmost(self):
           """Exported version of L{__notify_topmost}.
           """
           self.__lock.acquire()
           try:
             return self.__notify_topmost()
           finally:
             self.__lock.release()
         def delete(self, timeout=None, priority=None):
           """Delete a Shared Lock.
           This operation will declare the lock for removal. First the lock will be
           acquired in exclusive mode if you don't already own it, then the lock
           will be put in a state where any future and pending acquire() fail.
           @type timeout: float
           @param timeout: maximum waiting time before giving up
           @type priority: integer
           @param priority: Priority for acquiring lock
           """
           if priority is None:
             priority = _DEFAULT_PRIORITY
           self.__lock.acquire()
           try:
             assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
             self.__check_deleted()
             # The caller is allowed to hold the lock exclusively already.
             acquired = self.__is_exclusive()
             if not acquired:
               acquired = self.__acquire_unlocked(0, timeout, priority)
             if acquired:
               assert self.__is_exclusive() and not self.__is_sharer(), \
                 "Lock wasn't acquired in exclusive mode"
               self.__deleted = True
               self.__exc = None
               assert not (self.__exc or self.__shr), "Found owner during deletion"
               # Notify all acquires. They'll throw an error.
               for (_, prioqueue) in self.__pending:
                 for cond in prioqueue:
                   cond.notifyAll()
               assert self.__deleted
             return acquired
           finally:
             self.__lock.release()
         def _release_save(self):
           shared = self.__is_sharer()
           self.release()
           return shared
         def _acquire_restore(self, shared):
           self.acquire(shared=shared)
       # Whenever we want to acquire a full LockSet we pass None as the value
       # to acquire.  Hide this behind this nicely named constant.
       ALL_SET = None
       def _TimeoutZero():
         """Returns the number zero.
         """
         return 0
       def _GetLsAcquireModeAndTimeouts(want_all, timeout, opportunistic):
         """Determines modes and timeouts for L{LockSet.acquire}.
         @type want_all: boolean
         @param want_all: Whether all locks in set should be acquired
         @param timeout: Timeout in seconds or C{None}
         @param opportunistic: Whther locks should be acquired opportunistically
         @rtype: tuple
         @return: Tuple containing mode to be passed to L{LockSet.__acquire_inner}
           (one of L{_LS_ACQUIRE_MODES}), a function to calculate timeout for
           acquiring the lockset-internal lock (might be C{None}) and a function to
           calculate the timeout for acquiring individual locks
         """
         # Short circuit when no running timeout is needed
         if opportunistic and not want_all:
           assert timeout is None, "Got timeout for an opportunistic acquisition"
           return (_LS_ACQUIRE_OPPORTUNISTIC, None, _TimeoutZero)
         # We need to keep track of how long we spent waiting for a lock. The
         # timeout passed to this function is over all lock acquisitions.
         running_timeout = utils.RunningTimeout(timeout, False)
         if want_all:
           mode = _LS_ACQUIRE_ALL
           ls_timeout_fn = running_timeout.Remaining
         else:
           mode = _LS_ACQUIRE_EXACT
           ls_timeout_fn = None
         if opportunistic:
           mode = _LS_ACQUIRE_OPPORTUNISTIC
           timeout_fn = _TimeoutZero
         else:
           timeout_fn = running_timeout.Remaining
         return (mode, ls_timeout_fn, timeout_fn)
       class _AcquireTimeout(Exception):
         """Internal exception to abort an acquire on a timeout.
         """
       class LockSet:
         """Implements a set of locks.
         This abstraction implements a set of shared locks for the same resource type,
         distinguished by name. The user can lock a subset of the resources and the
         LockSet will take care of acquiring the locks always in the same order, thus
         preventing deadlock.
         All the locks needed in the same set must be acquired together, though.
         @type name: string
         @ivar name: the name of the lockset
         """
         def __init__(self, members, name, monitor=None):
           """Constructs a new LockSet.
           @type members: list of strings
           @param members: initial members of the set
           @type monitor: L{LockMonitor}
           @param monitor: Lock monitor with which to register member locks
           """
           assert members is not None, "members parameter is not a list"
           self.name = name
           # Lock monitor
           self.__monitor = monitor
           # Used internally to guarantee coherency
           self.__lock = SharedLock(self._GetLockName("[lockset]"), monitor=monitor)
           # The lockdict indexes the relationship name -> lock
           # The order-of-locking is implied by the alphabetical order of names
           self.__lockdict = {}
           for mname in members:
             self.__lockdict[mname] = SharedLock(self._GetLockName(mname),
                                                 monitor=monitor)
           # The owner dict contains the set of locks each thread owns. For
           # performance each thread can access its own key without a global lock on
           # this structure. It is paramount though that *no* other type of access is
           # done to this structure (eg. no looping over its keys). *_owner helper
           # function are defined to guarantee access is correct, but in general never
           # do anything different than __owners[threading.currentThread()], or there
           # will be trouble.
           self.__owners = {}
         def _GetLockName(self, mname):
           """Returns the name for a member lock.
           """
           return "%s/%s" % (self.name, mname)
         def _get_lock(self):
           """Returns the lockset-internal lock.
           """
           return self.__lock
         def _get_lockdict(self):
           """Returns the lockset-internal lock dictionary.
           Accessing this structure is only safe in single-thread usage or when the
           lockset-internal lock is held.
           """
           return self.__lockdict
         def is_owned(self):
           """Is the current thread a current level owner?
           @note: Use L{check_owned} to check if a specific lock is held
           """
           return threading.currentThread() in self.__owners
         def check_owned(self, names, shared=-1):
           """Check if locks are owned in a specific mode.
           @type names: sequence or string
           @param names: Lock names (or a single lock name)
           @param shared: See L{SharedLock.is_owned}
           @rtype: bool
           @note: Use L{is_owned} to check if the current thread holds I{any} lock and
             L{list_owned} to get the names of all owned locks
           """
           if isinstance(names, basestring):
             names = [names]
           # Avoid check if no locks are owned anyway
           if names and self.is_owned():
             candidates = []
             # Gather references to all locks (in case they're deleted in the meantime)
             for lname in names:
               try:
                 lock = self.__lockdict[lname]
               except KeyError:
                 raise errors.LockError("Non-existing lock '%s' in set '%s' (it may"
                                        " have been removed)" % (lname, self.name))
               else:
                 candidates.append(lock)
             return compat.all(lock.is_owned(shared=shared) for lock in candidates)
           else:
             return False
         def owning_all(self):
           """Checks whether current thread owns internal lock.
           Holding the internal lock is equivalent with holding all locks in the set
           (the opposite does not necessarily hold as it can not be easily
           determined). L{add} and L{remove} require the internal lock.
           @rtype: boolean
           """
           return self.__lock.is_owned()
         def _add_owned(self, name=None):
           """Note the current thread owns the given lock"""
           if name is None:
             if not self.is_owned():
               self.__owners[threading.currentThread()] = set()
           else:
             if self.is_owned():
               self.__owners[threading.currentThread()].add(name)
             else:
               self.__owners[threading.currentThread()] = set([name])
         def _del_owned(self, name=None):
           """Note the current thread owns the given lock"""
           assert not (name is None and self.__lock.is_owned()), \
                  "Cannot hold internal lock when deleting owner status"
           if name is not None:
             self.__owners[threading.currentThread()].remove(name)
           # Only remove the key if we don't hold the set-lock as well
           if not (self.__lock.is_owned() or
                   self.__owners[threading.currentThread()]):
             del self.__owners[threading.currentThread()]
         def list_owned(self):
           """Get the set of resource names owned by the current thread"""
           if self.is_owned():
             return self.__owners[threading.currentThread()].copy()
           else:
             return set()
         def _release_and_delete_owned(self):
           """Release and delete all resources owned by the current thread"""
           for lname in self.list_owned():
             lock = self.__lockdict[lname]
             if lock.is_owned():
               lock.release()
             self._del_owned(name=lname)
         def __names(self):
           """Return the current set of names.
           Only call this function while holding __lock and don't iterate on the
           result after releasing the lock.
           """
           return self.__lockdict.keys()
         def _names(self):
           """Return a copy of the current set of elements.
           Used only for debugging purposes.
           """
           # If we don't already own the set-level lock acquired
           # we'll get it and note we need to release it later.
           release_lock = False
           if not self.__lock.is_owned():
             release_lock = True
             self.__lock.acquire(shared=1)
           try:
             result = self.__names()
           finally:
             if release_lock:
               self.__lock.release()
           return set(result)
         def acquire(self, names, timeout=None, shared=0, priority=None,
                     opportunistic=False, test_notify=None):
           """Acquire a set of resource locks.
           @note: When acquiring locks opportunistically, any number of locks might
             actually be acquired, even zero.
           @type names: list of strings (or string)
           @param names: the names of the locks which shall be acquired
               (special lock names, or instance/node names)
           @type shared: integer (0/1) used as a boolean
           @param shared: whether to acquire in shared mode; by default an
               exclusive lock will be acquired
           @type timeout: float or None
           @param timeout: Maximum time to acquire all locks; for opportunistic
             acquisitions, a timeout can only be given when C{names} is C{None}, in
             which case it is exclusively used for acquiring the L{LockSet}-internal
             lock; opportunistic acquisitions don't use a timeout for acquiring
             individual locks
           @type priority: integer
           @param priority: Priority for acquiring locks
           @type opportunistic: boolean
           @param opportunistic: Acquire locks opportunistically; use the return value
             to determine which locks were actually acquired
           @type test_notify: callable or None
           @param test_notify: Special callback function for unittesting
           @return: Set of all locks successfully acquired or None in case of timeout
           @raise errors.LockError: when any lock we try to acquire has
               been deleted before we succeed. In this case none of the
               locks requested will be acquired.
           """
           assert timeout is None or timeout >= 0.0
           # Check we don't already own locks at this level
           assert not self.is_owned(), ("Cannot acquire locks in the same set twice"
                                        " (lockset %s)" % self.name)
           if priority is None:
             priority = _DEFAULT_PRIORITY
           try:
             if names is not None:
               assert timeout is None or not opportunistic, \
                 ("Opportunistic acquisitions can only use a timeout if no"
                  " names are given; see docstring for details")
               # Support passing in a single resource to acquire rather than many
               if isinstance(names, basestring):
                 names = [names]
               (mode, _, timeout_fn) = \
                 _GetLsAcquireModeAndTimeouts(False, timeout, opportunistic)
               return self.__acquire_inner(names, mode, shared, priority,
                                           timeout_fn, test_notify)
             else:
               (mode, ls_timeout_fn, timeout_fn) = \
                 _GetLsAcquireModeAndTimeouts(True, timeout, opportunistic)
               # If no names are given acquire the whole set by not letting new names
               # being added before we release, and getting the current list of names.
               # Some of them may then be deleted later, but we'll cope with this.
+              #
               # We'd like to acquire this lock in a shared way, as it's nice if
               # everybody else can use the instances at the same time. If we are
               # acquiring them exclusively though they won't be able to do this
               # anyway, though, so we'll get the list lock exclusively as well in
               # order to be able to do add() on the set while owning it.
               if not self.__lock.acquire(shared=shared, priority=priority,
                                          timeout=ls_timeout_fn()):
                 raise _AcquireTimeout()
               try:
                 # note we own the set-lock
                 self._add_owned()
                 return self.__acquire_inner(self.__names(), mode, shared,
                                             priority, timeout_fn, test_notify)
               except:
                 # We shouldn't have problems adding the lock to the owners list, but
                 # if we did we'll try to release this lock and re-raise exception.
                 # Of course something is going to be really wrong, after this.
                 self.__lock.release()
                 self._del_owned()
                 raise
           except _AcquireTimeout:
             return None
         def __acquire_inner(self, names, mode, shared, priority,
                             timeout_fn, test_notify):
           """Inner logic for acquiring a number of locks.
           Acquisition modes:
             - C{_LS_ACQUIRE_ALL}: C{names} contains names of all locks in set, but
               deleted locks can be ignored as the whole set is being acquired with
               its internal lock held
             - C{_LS_ACQUIRE_EXACT}: The names listed in C{names} must be acquired;
               timeouts and deleted locks are fatal
             - C{_LS_ACQUIRE_OPPORTUNISTIC}: C{names} lists names of locks (potentially
               all within the set) which should be acquired opportunistically, that is
               failures are ignored
           @param names: Names of the locks to be acquired
           @param mode: Lock acquisition mode (one of L{_LS_ACQUIRE_MODES})
           @param shared: Whether to acquire in shared mode
           @param timeout_fn: Function returning remaining timeout (C{None} for
             opportunistic acquisitions)
           @param priority: Priority for acquiring locks
           @param test_notify: Special callback function for unittesting
           """
           assert mode in _LS_ACQUIRE_MODES
           acquire_list = []
           # First we look the locks up on __lockdict. We have no way of being sure
           # they will still be there after, but this makes it a lot faster should
           # just one of them be the already wrong. Using a sorted sequence to prevent
           # deadlocks.
           for lname in sorted(frozenset(names)):
             try:
               lock = self.__lockdict[lname] # raises KeyError if lock is not there
             except KeyError:
               # We are acquiring the whole set, it doesn't matter if this particular
               # element is not there anymore. If, however, only certain names should
               # be acquired, not finding a lock is an error.
               if mode == _LS_ACQUIRE_EXACT:
                 raise errors.LockError("Lock '%s' not found in set '%s' (it may have"
                                        " been removed)" % (lname, self.name))
             else:
               acquire_list.append((lname, lock))
           # This will hold the locknames we effectively acquired.
           acquired = set()
           try:
             # Now acquire_list contains a sorted list of resources and locks we
             # want.  In order to get them we loop on this (private) list and
             # acquire() them.  We gave no real guarantee they will still exist till
             # this is done but .acquire() itself is safe and will alert us if the
             # lock gets deleted.
             for (lname, lock) in acquire_list:
               if __debug__ and callable(test_notify):
                 test_notify_fn = lambda: test_notify(lname)
               else:
                 test_notify_fn = None
               timeout = timeout_fn()
               try:
                 # raises LockError if the lock was deleted
                 acq_success = lock.acquire(shared=shared, timeout=timeout,
                                            priority=priority,
                                            test_notify=test_notify_fn)
               except errors.LockError:
                 if mode in (_LS_ACQUIRE_ALL, _LS_ACQUIRE_OPPORTUNISTIC):
                   # We are acquiring the whole set, it doesn't matter if this
                   # particular element is not there anymore.
                   continue
                 raise errors.LockError("Lock '%s' not found in set '%s' (it may have"
                                        " been removed)" % (lname, self.name))
               if not acq_success:
                 # Couldn't get lock or timeout occurred
                 if mode == _LS_ACQUIRE_OPPORTUNISTIC:
                   # Ignore timeouts on opportunistic acquisitions
                   continue
                 if timeout is None:
                   # This shouldn't happen as SharedLock.acquire(timeout=None) is
                   # blocking.
                   raise errors.LockError("Failed to get lock %s (set %s)" %
                                          (lname, self.name))
                 raise _AcquireTimeout()
               try:
                 # now the lock cannot be deleted, we have it!
                 self._add_owned(name=lname)
                 acquired.add(lname)
               except:
                 # We shouldn't have problems adding the lock to the owners list, but
                 # if we did we'll try to release this lock and re-raise exception.
                 # Of course something is going to be really wrong after this.
                 if lock.is_owned():
                   lock.release()
                 raise
           except:
             # Release all owned locks
             self._release_and_delete_owned()
             raise
           return acquired
         def downgrade(self, names=None):
           """Downgrade a set of resource locks from exclusive to shared mode.
           The locks must have been acquired in exclusive mode.
           """
           assert self.is_owned(), ("downgrade on lockset %s while not owning any"
                                    " lock" % self.name)
           # Support passing in a single resource to downgrade rather than many
           if isinstance(names, basestring):
             names = [names]
           owned = self.list_owned()
           if names is None:
             names = owned
           else:
             names = set(names)
             assert owned.issuperset(names), \
               ("downgrade() on unheld resources %s (set %s)" %
                (names.difference(owned), self.name))
           for lockname in names:
             self.__lockdict[lockname].downgrade()
           # Do we own the lockset in exclusive mode?
           if self.__lock.is_owned(shared=0):
             # Have all locks been downgraded?
             if not compat.any(lock.is_owned(shared=0)
                               for lock in self.__lockdict.values()):
               self.__lock.downgrade()
               assert self.__lock.is_owned(shared=1)
           return True
         def release(self, names=None):
           """Release a set of resource locks, at the same level.
           You must have acquired the locks, either in shared or in exclusive mode,
           before releasing them.
           @type names: list of strings, or None
           @param names: the names of the locks which shall be released
               (defaults to all the locks acquired at that level).
           """
           assert self.is_owned(), ("release() on lock set %s while not owner" %
                                    self.name)
           # Support passing in a single resource to release rather than many
           if isinstance(names, basestring):
             names = [names]
           if names is None:
             names = self.list_owned()
           else:
             names = set(names)
             assert self.list_owned().issuperset(names), (
                      "release() on unheld resources %s (set %s)" %
                      (names.difference(self.list_owned()), self.name))
           # First of all let's release the "all elements" lock, if set.
           # After this 'add' can work again
           if self.__lock.is_owned():
             self.__lock.release()
             self._del_owned()
           for lockname in names:
             # If we are sure the lock doesn't leave __lockdict without being
             # exclusively held we can do this...
             self.__lockdict[lockname].release()
             self._del_owned(name=lockname)
         def add(self, names, acquired=0, shared=0):
           """Add a new set of elements to the set
           @type names: list of strings
           @param names: names of the new elements to add
           @type acquired: integer (0/1) used as a boolean
           @param acquired: pre-acquire the new resource?
           @type shared: integer (0/1) used as a boolean
           @param shared: is the pre-acquisition shared?
           """
           # Check we don't already own locks at this level
           assert not self.is_owned() or self.__lock.is_owned(shared=0), \
             ("Cannot add locks if the set %s is only partially owned, or shared" %
              self.name)
           # Support passing in a single resource to add rather than many
           if isinstance(names, basestring):
             names = [names]
           # If we don't already own the set-level lock acquired in an exclusive way
           # we'll get it and note we need to release it later.
           release_lock = False
           if not self.__lock.is_owned():
             release_lock = True
             self.__lock.acquire()
           try:
             invalid_names = set(self.__names()).intersection(names)
             if invalid_names:
               # This must be an explicit raise, not an assert, because assert is
               # turned off when using optimization, and this can happen because of
               # concurrency even if the user doesn't want it.
               raise errors.LockError("duplicate add(%s) on lockset %s" %
                                      (invalid_names, self.name))
             for lockname in names:
               lock = SharedLock(self._GetLockName(lockname), monitor=self.__monitor)
               if acquired:
                 # No need for priority or timeout here as this lock has just been
                 # created
                 lock.acquire(shared=shared)
                 # now the lock cannot be deleted, we have it!
                 try:
                   self._add_owned(name=lockname)
                 except:
                   # We shouldn't have problems adding the lock to the owners list,
                   # but if we did we'll try to release this lock and re-raise
                   # exception.  Of course something is going to be really wrong,
                   # after this.  On the other hand the lock hasn't been added to the
                   # __lockdict yet so no other threads should be pending on it. This
                   # release is just a safety measure.
                   lock.release()
                   raise
               self.__lockdict[lockname] = lock
           finally:
             # Only release __lock if we were not holding it previously.
             if release_lock:
               self.__lock.release()
           return True
         def remove(self, names):
           """Remove elements from the lock set.
           You can either not hold anything in the lockset or already hold a superset
           of the elements you want to delete, exclusively.
           @type names: list of strings
           @param names: names of the resource to remove.
           @return: a list of locks which we removed; the list is always
               equal to the names list if we were holding all the locks
               exclusively
           """
           # Support passing in a single resource to remove rather than many
           if isinstance(names, basestring):
             names = [names]
           # If we own any subset of this lock it must be a superset of what we want
           # to delete. The ownership must also be exclusive, but that will be checked
           # by the lock itself.
           assert not self.is_owned() or self.list_owned().issuperset(names), (
             "remove() on acquired lockset %s while not owning all elements" %
             self.name)
           removed = []
           for lname in names:
             # Calling delete() acquires the lock exclusively if we don't already own
             # it, and causes all pending and subsequent lock acquires to fail. It's
             # fine to call it out of order because delete() also implies release(),
             # and the assertion above guarantees that if we either already hold
             # everything we want to delete, or we hold none.
             try:
               self.__lockdict[lname].delete()
               removed.append(lname)
             except (KeyError, errors.LockError):
               # This cannot happen if we were already holding it, verify:
               assert not self.is_owned(), ("remove failed while holding lockset %s" %
                                            self.name)
             else:
               # If no LockError was raised we are the ones who deleted the lock.
               # This means we can safely remove it from lockdict, as any further or
               # pending delete() or acquire() will fail (and nobody can have the lock
               # since before our call to delete()).
+              #
               # This is done in an else clause because if the exception was thrown
               # it's the job of the one who actually deleted it.
               del self.__lockdict[lname]
               # And let's remove it from our private list if we owned it.
               if self.is_owned():
                 self._del_owned(name=lname)
           return removed
       # Locking levels, must be acquired in increasing order. Current rules are:
       # - At level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
       #   acquired before performing any operation, either in shared or exclusive
       #   mode. Acquiring the BGL in exclusive mode is discouraged and should be
       #   avoided..
       # - At levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks. If
       #   you need more than one node, or more than one instance, acquire them at the
       #   same time.
       # - LEVEL_NODE_RES is for node resources and should be used by operations with
       #   possibly high impact on the node's disks.
       # - LEVEL_NODE_ALLOC blocks instance allocations for the whole cluster
       #   ("NAL" is the only lock at this level). It should be acquired in shared
       #   mode when an opcode blocks all or a significant amount of a cluster's
       #   locks. Opcodes doing instance allocations should acquire in exclusive mode.
       #   Once the set of acquired locks for an opcode has been reduced to the working
       #   set, the NAL should be released as well to allow allocations to proceed.
       (LEVEL_CLUSTER,
        LEVEL_INSTANCE,
        LEVEL_NODE_ALLOC,
        LEVEL_NODEGROUP,
        LEVEL_NODE,
        LEVEL_NODE_RES,
        LEVEL_NETWORK) = range(0, 7)
       LEVELS = [
         LEVEL_CLUSTER,
         LEVEL_INSTANCE,
         LEVEL_NODE_ALLOC,
         LEVEL_NODEGROUP,
         LEVEL_NODE,
         LEVEL_NODE_RES,
         LEVEL_NETWORK,
+        ]
       # Lock levels which are modifiable
       LEVELS_MOD = compat.UniqueFrozenset([
         LEVEL_NODE_RES,
         LEVEL_NODE,
         LEVEL_NODEGROUP,
         LEVEL_INSTANCE,
         LEVEL_NETWORK,
         ])
       #: Lock level names (make sure to use singular form)
       LEVEL_NAMES = {
         LEVEL_CLUSTER: "cluster",
         LEVEL_INSTANCE: "instance",
         LEVEL_NODE_ALLOC: "node-alloc",
         LEVEL_NODEGROUP: "nodegroup",
         LEVEL_NODE: "node",
         LEVEL_NODE_RES: "node-res",
         LEVEL_NETWORK: "network",
+        }
       # Constant for the big ganeti lock
       BGL = "BGL"
       #: Node allocation lock
       NAL = "NAL"
       class GanetiLockManager:
         """The Ganeti Locking Library
         The purpose of this small library is to manage locking for ganeti clusters
         in a central place, while at the same time doing dynamic checks against
         possible deadlocks. It will also make it easier to transition to a different
         lock type should we migrate away from python threads.
         """
         _instance = None
         def __init__(self, node_uuids, nodegroups, instance_names, networks):
           """Constructs a new GanetiLockManager object.
           There should be only a GanetiLockManager object at any time, so this
           function raises an error if this is not the case.
           @param node_uuids: list of node UUIDs
           @param nodegroups: list of nodegroup uuids
           @param instance_names: list of instance names
           """
           assert self.__class__._instance is None, \
                  "double GanetiLockManager instance"
           self.__class__._instance = self
           self._monitor = LockMonitor()
           # The keyring contains all the locks, at their level and in the correct
           # locking order.
           self.__keyring = {
             LEVEL_CLUSTER: LockSet([BGL], "cluster", monitor=self._monitor),
             LEVEL_NODE: LockSet(node_uuids, "node", monitor=self._monitor),
             LEVEL_NODE_RES: LockSet(node_uuids, "node-res", monitor=self._monitor),
             LEVEL_NODEGROUP: LockSet(nodegroups, "nodegroup", monitor=self._monitor),
             LEVEL_INSTANCE: LockSet(instance_names, "instance",
                                     monitor=self._monitor),
             LEVEL_NETWORK: LockSet(networks, "network", monitor=self._monitor),
             LEVEL_NODE_ALLOC: LockSet([NAL], "node-alloc", monitor=self._monitor),
+            }
           assert compat.all(ls.name == LEVEL_NAMES[level]
                             for (level, ls) in self.__keyring.items()), \
             "Keyring name mismatch"
         def AddToLockMonitor(self, provider):
           """Registers a new lock with the monitor.
           See L{LockMonitor.RegisterLock}.
           """
           return self._monitor.RegisterLock(provider)
         def QueryLocks(self, fields):
           """Queries information from all locks.
           See L{LockMonitor.QueryLocks}.
           """
           return self._monitor.QueryLocks(fields)
         def _names(self, level):
           """List the lock names at the given level.
           This can be used for debugging/testing purposes.
           @param level: the level whose list of locks to get
           """
           assert level in LEVELS, "Invalid locking level %s" % level
           return self.__keyring[level]._names()
         def is_owned(self, level):
           """Check whether we are owning locks at the given level
           """
           return self.__keyring[level].is_owned()
         def list_owned(self, level):
           """Get the set of owned locks at the given level
           """
           return self.__keyring[level].list_owned()
         def check_owned(self, level, names, shared=-1):
           """Check if locks at a certain level are owned in a specific mode.
           @see: L{LockSet.check_owned}
           """
           return self.__keyring[level].check_owned(names, shared=shared)
         def owning_all(self, level):
           """Checks whether current thread owns all locks at a certain level.
           @see: L{LockSet.owning_all}
           """
           return self.__keyring[level].owning_all()
         def _upper_owned(self, level):
           """Check that we don't own any lock at a level greater than the given one.
           """
           # This way of checking only works if LEVELS[i] = i, which we check for in
           # the test cases.
           return compat.any((self.is_owned(l) for l in LEVELS[level + 1:]))
         def _BGL_owned(self): # pylint: disable=C0103
           """Check if the current thread owns the BGL.
           Both an exclusive or a shared acquisition work.
           """
           return BGL in self.__keyring[LEVEL_CLUSTER].list_owned()
         @staticmethod
         def _contains_BGL(level, names): # pylint: disable=C0103
           """Check if the level contains the BGL.
           Check if acting on the given level and set of names will change
           the status of the Big Ganeti Lock.
           """
           return level == LEVEL_CLUSTER and (names is None or BGL in names)
         def acquire(self, level, names, timeout=None, shared=0, priority=None,
                     opportunistic=False):
           """Acquire a set of resource locks, at the same level.
           @type level: member of locking.LEVELS
           @param level: the level at which the locks shall be acquired
           @type names: list of strings (or string)
           @param names: the names of the locks which shall be acquired
               (special lock names, or instance/node names)
           @type shared: integer (0/1) used as a boolean
           @param shared: whether to acquire in shared mode; by default
               an exclusive lock will be acquired
           @type timeout: float
           @param timeout: Maximum time to acquire all locks
           @type priority: integer
           @param priority: Priority for acquiring lock
           @type opportunistic: boolean
           @param opportunistic: Acquire locks opportunistically; use the return value
             to determine which locks were actually acquired
           """
           assert level in LEVELS, "Invalid locking level %s" % level
           # Check that we are either acquiring the Big Ganeti Lock or we already own
           # it. Some "legacy" opcodes need to be sure they are run non-concurrently
           # so even if we've migrated we need to at least share the BGL to be
           # compatible with them. Of course if we own the BGL exclusively there's no
           # point in acquiring any other lock, unless perhaps we are half way through
           # the migration of the current opcode.
           assert (self._contains_BGL(level, names) or self._BGL_owned()), (
             "You must own the Big Ganeti Lock before acquiring any other")
           # Check we don't own locks at the same or upper levels.
           assert not self._upper_owned(level), ("Cannot acquire locks at a level"
                                                 " while owning some at a greater one")
           # Acquire the locks in the set.
           return self.__keyring[level].acquire(names, shared=shared, timeout=timeout,
                                                priority=priority,
                                                opportunistic=opportunistic)
         def downgrade(self, level, names=None):
           """Downgrade a set of resource locks from exclusive to shared mode.
           You must have acquired the locks in exclusive mode.
           @type level: member of locking.LEVELS
           @param level: the level at which the locks shall be downgraded
           @type names: list of strings, or None
           @param names: the names of the locks which shall be downgraded
               (defaults to all the locks acquired at the level)
           """
           assert level in LEVELS, "Invalid locking level %s" % level
           return self.__keyring[level].downgrade(names=names)
         def release(self, level, names=None):
           """Release a set of resource locks, at the same level.
           You must have acquired the locks, either in shared or in exclusive
           mode, before releasing them.
           @type level: member of locking.LEVELS
           @param level: the level at which the locks shall be released
           @type names: list of strings, or None
           @param names: the names of the locks which shall be released
               (defaults to all the locks acquired at that level)
           """
           assert level in LEVELS, "Invalid locking level %s" % level
           assert (not self._contains_BGL(level, names) or
                   not self._upper_owned(LEVEL_CLUSTER)), (
                     "Cannot release the Big Ganeti Lock while holding something"
                     " at upper levels (%r)" %
                     (utils.CommaJoin(["%s=%r" % (LEVEL_NAMES[i], self.list_owned(i))
                                       for i in self.__keyring.keys()]), ))
           # Release will complain if we don't own the locks already
           return self.__keyring[level].release(names)
         def add(self, level, names, acquired=0, shared=0):
           """Add locks at the specified level.
           @type level: member of locking.LEVELS_MOD
           @param level: the level at which the locks shall be added
           @type names: list of strings
           @param names: names of the locks to acquire
           @type acquired: integer (0/1) used as a boolean
           @param acquired: whether to acquire the newly added locks
           @type shared: integer (0/1) used as a boolean
           @param shared: whether the acquisition will be shared
           """
           assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
           assert self._BGL_owned(), ("You must own the BGL before performing other"
                                      " operations")
           assert not self._upper_owned(level), ("Cannot add locks at a level"
                                                 " while owning some at a greater one")
           return self.__keyring[level].add(names, acquired=acquired, shared=shared)
         def remove(self, level, names):
           """Remove locks from the specified level.
           You must either already own the locks you are trying to remove
           exclusively or not own any lock at an upper level.
           @type level: member of locking.LEVELS_MOD
           @param level: the level at which the locks shall be removed
           @type names: list of strings
           @param names: the names of the locks which shall be removed
               (special lock names, or instance/node names)
           """
           assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
           assert self._BGL_owned(), ("You must own the BGL before performing other"
                                      " operations")
           # Check we either own the level or don't own anything from here
           # up. LockSet.remove() will check the case in which we don't own
           # all the needed resources, or we have a shared ownership.
           assert self.is_owned(level) or not self._upper_owned(level), (
                  "Cannot remove locks at a level while not owning it or"
                  " owning some at a greater one")
           return self.__keyring[level].remove(names)
       def _MonitorSortKey((item, idx, num)):
         """Sorting key function.
         Sort by name, registration order and then order of information. This provides
         a stable sort order over different providers, even if they return the same
         name.
         """
         (name, _, _, _) = item
         return (utils.NiceSortKey(name), num, idx)
       class LockMonitor(object):
         _LOCK_ATTR = "_lock"
         def __init__(self):
           """Initializes this class.
           """
           self._lock = SharedLock("LockMonitor")
           # Counter for stable sorting
           self._counter = itertools.count(0)
           # Tracked locks. Weak references are used to avoid issues with circular
           # references and deletion.
           self._locks = weakref.WeakKeyDictionary()
         @ssynchronized(_LOCK_ATTR)
         def RegisterLock(self, provider):
           """Registers a new lock.
           @param provider: Object with a callable method named C{GetLockInfo}, taking
             a single C{set} containing the requested information items
           @note: It would be nicer to only receive the function generating the
             requested information but, as it turns out, weak references to bound
             methods (e.g. C{self.GetLockInfo}) are tricky; there are several
             workarounds, but none of the ones I found works properly in combination
             with a standard C{WeakKeyDictionary}
           """
           assert provider not in self._locks, "Duplicate registration"
           # There used to be a check for duplicate names here. As it turned out, when
           # a lock is re-created with the same name in a very short timeframe, the
           # previous instance might not yet be removed from the weakref dictionary.
           # By keeping track of the order of incoming registrations, a stable sort
           # ordering can still be guaranteed.
           self._locks[provider] = self._counter.next()
         def _GetLockInfo(self, requested):
           """Get information from all locks.
           """
           # Must hold lock while getting consistent list of tracked items
           self._lock.acquire(shared=1)
           try:
             items = self._locks.items()
           finally:
             self._lock.release()
           return [(info, idx, num)
                   for (provider, num) in items
                   for (idx, info) in enumerate(provider.GetLockInfo(requested))]
         def _Query(self, fields):
           """Queries information from all locks.
           @type fields: list of strings
           @param fields: List of fields to return
           """
           qobj = query.Query(query.LOCK_FIELDS, fields)
           # Get all data with internal lock held and then sort by name and incoming
           # order
           lockinfo = sorted(self._GetLockInfo(qobj.RequestedData()),
                             key=_MonitorSortKey)
           # Extract lock information and build query data
           return (qobj, query.LockQueryData(map(compat.fst, lockinfo)))
         def QueryLocks(self, fields):
           """Queries information from all locks.
           @type fields: list of strings
           @param fields: List of fields to return
           """
           (qobj, ctx) = self._Query(fields)
           # Prepare query response
           return query.GetQueryResponse(qobj, ctx)

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